Transmission Lubricants (Part2)
by Ken Gillanders

One thing about racing; technology is rampant and sometimes we get poor or confusing results. About two years ago, one or two of the current crop of TR racers and a good number of TR owners whose cars are street-driven only began using synthetic gear oils in the gearbox to reduce friction. This did in fact reduce friction by a small but measureable degree, with an equal rise in available power.

Toward the end of last year’s vintage racing season problems began to develop in two particular areas. First, the race drivers noticed that virtually all the TR’s using synthetic gear oil developed a tendency to jump out out of third gear while braking hard downhill. We disassembled a gearbox that had been doing this and found that it could be made to jump out of third gear while performing a simple test out of the car. We held the gearbox vertically in the air and released it, stopping it just short of hitting the ground, at which point it would snap out of third. Making some adjustments on the detent springs and balls in the synchro hub reduced this tendency, but could not completely prevent it. It then became apparent that the combined weights of the shifter shaft, fork and the outer ring of the 3/4 synchro was enough to overcome the resistance of the detent and the ‘box would jump out of gear. We tried changing to a normal gear oil and found that it no longer jumped out of gear.

The second problem with the use of synthetic gear oil came when we noticed that when racing on short, twisting courses where first gear was needed repeatedly, it became increasingly harder to get into first. After about 20-30 engagements, it became progressively more difficult until it could no longer be engaged at all. After we took apart a box that had this problem we found that the synthetic oil was so slick that the heavier gears could not be stopped by the synchro rings. The steel gears were grinding off the pointed teeth until they were flat, preventing engagement. The heavier the gear, the more inertia we had to deal with; first gear is so heavy that its synchro ring failed first.

The cure is to stop using super slick gear oils and change to a standard 80-90 weight gear oil in non-overdrive gearboxes, or 20-50 engine oil (Valvoline Racing is a good brand) in the OD-equipped units.